Husband keeping secrets


So I really just want to post this to vent so keep your nagititive comments to yourself please. My husband and I switched to an online bank after we got married in September. Do the only way to see your transaction history is to go online or on the app. My phone was to low on storage so I couldn't download the app. So I didn't see pur transaction history for about 3 months. My husband is was the only one who had the app. I got a new phone for Christmas so I downloaded the bank app. I looked at our transaction history and I see my husband sent to $200 to this company. I asked what is this? He explained how he had been investing in stocks on this app on his phone. I am just really hurt that be kept this a secret from me. I tell my husband everything. We're married and share our finances. Why would he not tell me?? And how much money would he have invested if I hadn't of caught him?? I just feel like it was so immature of him to not tell me. And it makes me wonder what else he could be hiding?